The present invention relates to a supersensitive nuclear magnetic resonance imaging apparatus; and, more particularly, the invention relates to an apparatus for effecting a high resolution imaging of biosamples, such as cells, organic tissues, laboratory small animals, or the like, and to growth of a high-grade protein crystal using high resolution imaging, on-site observation of the process of growth, and a method of growth.
In recent years, rapid advances have been made in an imaging method utilizing nuclear magnetic resonance (NMR) imaging. If an analysis of the metabolism of cells or a protein information network in living organisms, such as human bodies, small animals, or cellular structures, can be made possible in the future by combining the NMR method and a powerful superconducting magnet technology, it will be possible for the structure or function of the protein in cells to be revealed. Thus, there are great hopes that this technology may play a great roll in the study of life science, such as the prevention of disease or the development of new drugs. In recent years, effective analysis of the structure of an organic compound, such as a protein, which has a complicated molecular structure, at the bioatomic level, became possible by the use of nuclear magnetic resonance spectroscopy.
The object of the present invention is to provide a supersensitive nuclear magnetic resonance imaging apparatus having spatial resolutions not more than 1 micron, and, more preferably, in the order of 0.1 micron, which is required for enabling an analysis of the metabolism of cells or the protein information network in cells in living organisms, such as small animals or cellular structures, that corresponds to a special imaging apparatus requiring a high performance that is three digits higher in spatial resolution, at least one digit higher in field strength of a superconducting magnet, four digits higher in uniformity of the magnetic fields, and three digits higher in stability in comparison with a medical MRI image diagnostic apparatus of the type used for laminagraphy of human bodies, which requires an image resolution in the so-called millimeter category, thus requiring completely different design technology and apparatus manufacturing technology.
Heretofore, a nuclear magnetic resonance imaging apparatus has been used as a medical image diagnostic apparatus having a field strength in the range of 0.2 to 8 T for application to a partial or entire human body, and, generally, magnetic fields in the order of 0.3 to 1.5 Tesla are used in many cases. A detailed description of the latest technology relating to such a nuclear magnetic resonance imaging apparatus is described in “MR imaging technology” by the Japanese Society of Radiological Technology, published by Ohmsha, 2001. In imaging utilizing a superconducting magnet, magnetic fields of not less than 0.5 Tesla are utilized, and the spatial resolution of images in the medical nuclear magnetic resonance image diagnostic apparatus is generally 0.2 mm.
A spectroscopic apparatus using high magnetic fields in the order of 14 to 21 T for the purpose of utilizing a nuclear magnetic resonance analyzing method for analyzing the structure of organic matter or protein also has been developed. The latest developments relating to a typical apparatus structure to be used in the case of employing such a high-magnetic-field NMR in nuclear magnetic resonance imaging includes the technology relating to a superconducting magnet disclosed in JP-A-2000-147082, which describes a typical structure of a multi-layer hollow solenoid coil; the technology relating to signal detection as described in U.S. Pat. No. 6,121,776, which describes a birdcage superconducting detector coil; and the technology disclosed in JP-A-2000-266830 and in JP-A-6-237912 which describe signal detecting using saddle type coils or birdcage coils. According to the descriptions provided in these publications, a high resolution nuclear magnetic resonance analyzing apparatus employs a superconducting magnetic apparatus constructed of a combination of solenoid coils that generate magnetic fields in the vertical direction for irradiating an electromagnetic wave of 400 to 900 MHz to a sample and detecting a resonant wave generated by the sample by the use of a saddle type or a birdcage type of detector coils. There is also a case in which, as shown in the example disclosed in U.S. Pat. No. 6,121,776, a detector that is cooled to low temperatures for reducing heat noise generated when receiving the resonant wave is used for improving the S/N sensitivity ratio.
Historically, the nuclear magnetic resonance spectroscopic apparatus has been improved in its sensitivity basically by maintaining the same basic system structure, such as the antenna, magnet, and the like, while increasing the central magnetic field strength of the superconducting magnet. Therefore, though the highest NMR measurement sensitivity reported thus far is obtained by an NMR apparatus of 900 MHz using a large superconducting magnet having a central magnetic field of 21.1 Tesla, the basic structure of the apparatus is no different from that described in JP-A-2000-147082. With a protein in solution being generally used as a sample, improvement of the central magnetic field has effects on improvement of the sensitivity in NMR spectroscopy and on identification of the separation of a chemical shift.
As regards the effect of improvement of the sensitivity due to the configuration of the detector coil, as described on P.326 of “The NMR” written by Yoji ARATA, published by Maruzen, 2000, it has been known that employing a solenoid coil as a detector coil brings about various advantages in comparison with the case where a saddle type or birdcage type coil is used. For example, a solenoid coil is known to be superior in impedance controllability, filling factors, and in the efficiency of the RF magnetic field which it produces. According to this publication, however, when the sensitivity is important, as in the case of measuring a minute amount of protein dissolved in an aqueous solution, it is impossible to wind a solenoid coil around a sample tube placed with a vertical orientation with respect to the magnetic field in the currently available superconducting magnet structure as a matter of fact, and thus such a coil is not generally used. As an exception, there is a case in which it is used in a limited manner for a sensitive measurement using a minute amount of sample solution, and a method of measuring with a specially designed micro sample tube and a specific probe is known.
In a specific example, JP-A-11-248810 discloses a method of magnetizing a high temperature superconducting bulk magnet in the horizontal direction, and the NMR signal is detected by means of a solenoid coil. Alternatively, JP-A-7-240310 discloses a method of constructing a superconducting magnet and a cooling container suitable for use in general NMR imaging for eliminating the limitation of the height of the apparatus due to the height of the ceiling. However, a method of improving the detection sensitivity required for high resolution imaging and a technical application for obtaining a uniformity of the magnetic fields or time-based stability of the magnetic field are not disclosed.
Remarkable progress has been made in recent years in the life sciences, but an understanding of the correlation between the function and the structure of a protein molecule at the biocellular level is not sufficient. Though there exist about 1011 kinds of protein in the natural world, protein molecules having a structure which is known only number in the order of 103-4 kinds, and studies utilizing high resolution NMR imaging, such as metabolism in a living organism, clarification of a protein communication network, or the like, have just started.
In addition, it is quite important for the progress of the life sciences to obtain a high-quality monocrystal of protein, but the growth of a high-quality protein crystal that can be analyzed sufficiently is still difficult, and the growth thereof requires several months to several years. The principal factor responsible for this difficulty consists in the fact that crystallization of a protein is carried out by a cut-and-try method that relies on experience. Though the mechanism of protein crystal growth has been examined since the middle of the 1980's, what is known at the present time is that the basic mechanism of crystal growth can be explained by the same mechanism irrespective of whether it is inorganic or organic, or low molecular or high molecular. High resolution NMR imaging is considered to be usable for clarification of such a mechanism of protein crystal growth or automation or optimization of the control of growth conditions.
Recently, the study of a life mechanism using cells in a living organism, living body tissues, small animals, and the like was made in association with an increase in the need to advance life science studies. If the metabolism of a protein in the living body, or the information network of the same, can be clarified by the use of a nuclear magnetic resonance imaging method, it is considered that worthwhile effects can be obtained in the advancement of the life sciences. However, the spatial resolution of the current nuclear magnetic resonance analyzing apparatus is generally 0.2 mm, and thus a minute area in the order of 1 to 10 micron, which represents the sizes of cells, cannot be imaged.
Accordingly, the present invention provides a method of enabling imaging of images on a scale one digit smaller than the cell size. Applying such a method and enabling it to be used for analyzing the metabolism of cells of living organisms or a bioinfomatic network, or on-site protein crystal growth significantly contributes to the development of the life sciences.
In order to adapt a nuclear magnetic resonance analyzing apparatus to such needs, it is required to improve the measurement sensitivity, while maintaining a sample space which meets the study needs in biology, and ensuring the stability of superconducting magnetic fields is also essential. Improvement of the measurement sensitivity and the uniformity of the magnetic fields in the sample space are important to improve the spatial resolution. Therefore, the nuclear magnet resonance analyzing apparatus that will be used for analyses in the study based on molecular biology in the future should be designated as a “nuclear magnetic resonance imaging” apparatus, which requires exceptional detection sensitivity and stability and the capability of detecting an NMR signal stably in comparison with the conventional NMR apparatus. When the magnetic fields are not uniform, problems, such as difficulty in identification of images, may occur. Therefore, it should be noted that NMR technology in the future, as directed to various analyses in the study of molecular biology, requires a new development of technology that is not the simple continuation of the general NMR apparatus of the type currently available.
For example, the specification of uniformity of the magnetic fields in the general NMR apparatus is 0.01 ppm in a sample space and 0.01 ppm/h in time-based stability. When converting these values by Proton NMR of 600 MHz for general use, the allowable error is 6 Hz. However, the aforementioned nuclear magnetic resonance imaging requires a space and time-based resolution of at least 1.0 Hz or less, and preferably, 0.5 Hz or less. The superconducting magnet or the detector coil must be optimally constructed in such a manner that such a uniformity of the magnetic field and time-based stability can be realized. Therefore, the performance of the NMR apparatus that has been generally used to date is not sufficient, and thus a stability and uniformity of the magnetic field that is one digit higher are required.
In the currently available apparatus, there arose a problem of installability such that a specific building was necessary because the apparatus was increased in size as the sensitivity was improved, relying mainly upon the improvement of the strength of the magnetic field, and thus leakage of the magnetic field and the necessity of providing a strong floor to support the apparatus had to be considered. In addition, there arose considerations that caused the costs of the superconducting magnet to increase. In this method, improvement of the sensitivity reaches generally 21T, which is the upper limit value under the constraint of the critical magnetic field of superconducting material. Therefore, technology to improve the detection sensitivity by a novel measure that does not rely upon the magnetic field strength has been anticipated in order to achieve greater improvement of the sensitivity.
As has been described above, a method of supersensitive measurement using a solenoid coil can be performed only with a minute quantity of a specific sample and with the use of a specific detector probe, but it cannot be applied to cell imaging due to the issue of resolution. As in the example disclosed in JP-A-11-248810, in a system in which a magnetic field was generated in the horizontal direction with a strong magnet and a NMR signal was detected with a solenoid coil, only a magnetic field less than 10T could be generated on the surface of a high temperature superconducting body, and the magnetic field in the portion of the sample was several Tesla at the highest. Therefore, using this method, it was impossible to generate a magnetic field not less than 11 Tesla, such as is required for the imaging of cells, or preferably, not less than 14.1 Tesla, in the desired sample space. Further, in using this method, it was very difficult to achieve a time-based stability of 1.0 Hz/h or less, that is required for the imaging of cells, due to the effect of a magnetic flux creeping phenomenon of the high temperature superconducting body. As regards the uniformity of the magnetic field required for analysis of protein, it was also difficult to achieve a uniformity of the magnetic field in the level less than 1.0 Hz in Proton nuclear magnetic resonance frequencies in a space of 10 mm (diameter)×10 mm (length), because of the non-uniformity caused by the process of manufacture of the high temperature superconducting bulk body material.
As has been described thus far, in the related technical field, while development of a breakthrough technology for accommodating the need for analysis of a protein was required, a novel solution for greater improvement of the sensitivity at the present time that the limit of improvement of sensitivity in the magnetic field is already attained has been expected.
In the case where analysis using on-site observation of the metabolic reaction in the cells or imaging of a protein information network, which is considered to be increasingly required in the future, is performed effectively and accurately, experientially, it is desirable to be able to effect a measurement at 600 to 900 MHz, with 14 to 21 T at the central magnetic field, and with an appropriate amount of sample, and to obtain a sensitivity of measurement higher than the status quo and simultaneously to increase the throughput.